Radio direction finder



1943- M. G. LlMB 2,328,024

RADIO DIRECTION FINDER Filed May 6', 1942 2 Sheets-Sheet 1 \nvenTor. Marcus G.LimbbyM 1 3- M. G. LIMB 2,328,024

RADIO DIRECTION FINDER Filed May 6, 1942 2 Sheets-Sheet 2 Fig.4. 4' 9 \nvenToT.

Marcus G L-imb by mdww Patented Aug. 31, 1943 This invention relates veto l a ;xnu lti fjnequen ;y;

radio direction finder, and; particularly to -{the loop-antenna thereof.

One of the objects: of. the pr sent invention: i

to provide a novel direction-a1 -loopeantenna which; is so, constructed that it can be madepto,

resonate. equally Well on any. one; of a plu-ryalitmoi frequency bands, and at the sametime maintam an optimum number of turns in the leopwindme; for the purpose of keeping the; eiiective-height oisaidwindingiata-maximum consistent; with its diameter for agiven frequency band Thisobject is accomplished-by making the loop antenna} two ormore sections-of substantiallythe same 1 diameter; said; sections 'preferably h u h: not n c a y, h ving-a d rentfn m er of; th .v l esf; the windings t twoloop sectionsbeing. so related to each other,

that when-all the loopsections are connected parallel, the inductance of zthe entire 1c'0p- -antenna is; ,such that; it will resonateefieetivelypn he "h hest of a plu a it p re uency. b d

W il Whenallthkeloop-eections are connectedin series, the inductance of the; entireizlo opaanten na iszsuch thattit will resonate"efiectively omai lowerhfnequency band. By introducing a: loading coil; into theseniesecnnneciiedrlwp sections, said loop -antenna; will. resonate: on; a, stillLlQWET-afi-Ie-f quency band. In ea-eh:,,case. however: the loop-cincuit. has: the optimum number of turns as: it; waysinc'ludeszbothloop-sections; .4

As stated-above, the:loopantenne may'bewmade in more than two sections, and: it: the antenna" hasthree onmoresectionsithe-said: antenna-may beadjusted' to resonate eifectively on sti11 ''othev frequency bands hy connecti'ng the antenna-sections partially in parallel and; {partially in series By way of example and'assur'ning thatfthe lo'op antenna hastwosections'ythese two loop section's may'be so wound that .when they are connected in parallel, the loop antenna will; resonateefiec tively on a shortwave frequency band of 1240 to 3000 kc, andwhen the two loop sections} are connected in series,1-' the loop antenna ljfresoe natefefi'ectively ontheregular broadca Y 5:40 to125qke;wm1e when 1th] loading 1 1;

the-invention iswequal lyappl ic ablio nee ienw h her s wfier rnth re ngs added" to the series-connected looplsje tic s the Fig. 1- 1; tion finder embodying r m-invention.

i F 21 a d agramma v ewo n the rci-litsof.theloop-antenna,

tionin which the lopp antenna is composedflof tune} illustrating construction-1* ieatures of the loop antenna.

Fig. 5 is a side jl-iew oi the sunportingiirame V forthefantennawith part broken out .ipigssfiise section on the linear-angle,

I Y Qfithe drawings, ,llindicatesugeneraliy theantenna loop-structure ofa-radio dirlection v I .finder and 2. is the receiver which isbrovided v with' fthe' usual {controls 3.1 The loop-antenna I structure. I is mounted'on. the receiver: housing 1 forlt'urning movement about. a vertical, axisaasQ u sua lfin' devices of thi's..' c1ass,j and it is herein shown as. having a comb'as's 4f. mounted. therein,

thisibeinga structure similar-to 'thatsshown in .Figs.'2a;n'd4,'the"1o i which are indicated at B'an'dt respectiveiy, both sections beingwound' aio'outthe m mos; "lf'off the t .-supportingflframe-and-being situated. between) sidemembersfi 'The section8*hasa1esser humher-of "turns' than-the section 9*, therelativevaiue L of-"these'two p sectionsbeing determined hy the characteref the differentfrequencyhands In my. improued; antenna structure the anten- I nanlobp "is made in; alplurality of secti'onslwl'lich have. substantiallythefsame' diameter a'nd are-{herein shown as having. a different number of'turns; Theselloop sections are wound on; a su'liporting'fiamefi which illustrated; as. eomprising, two annular" sid'ei member's 6?. that are I s'paceiapart andare gconnected by tie r'o plantenna. has two. 5

withwhich itFiswdes ir-edto use the instrument. All th'e turns of both-loop sections-E and 9 "however-, have substantially the same diameter as theyare woundlomthegsame frame andztheyhzlso hawe a; common-axiss 'l he tw-oends -I when: H: of the: antenna iL-loop circuit, which J mclud'esi both". 1 loom-sections; and thus; has anoptimum'a' number; ofrsturnsy at substantially the vsame; diam'euer are connected: tor the twoz'sides t2: and I 22; the: circuiti leadingto the receiver:thmughstheimedium I offla commutator-ofrusuai-construction; compris 7 e V me hestwoeolleqton ringsul'3 -and: Hf; theicollec I tpn ring; 8 jbeingt connected-to the: circuit con-Y nectionsztns of. the: icon-:circuitand thepzcollector, fine. !fiv e n ec n teettmthe: 1 puit an ction" a Q.'@ 1,=Q "91 i ,Th acirc. en e ions z r a; ,nerspective View of a: radio direc- Fig; e is a vrew pa tial-1y diagrammatic inna and l2a of the receiver circuit are connected to the collector rings l3 and I4 through usual brushes indicated at l5, this being a well-known construction for maintaining the circuit connections between the loop circuit and the receiver circuit as the directional loop antenna of a radio direction finder is turned about its vertical axis in order to set it for minimum signal recepceiving set per se, I have not thought it neces sary to illustrate more of the receiving set than is shown in the drawings. a 1 5 Means, such as a switch mechanism A, is provided for connecting the loop sections 8 and 9 either in parallel or in series, and, as stated above, the relative values of; the two loop sections are such that when they areconnected in parallel, the entire loop antenna has an inductance such that it will resonate effectively on a higher fre-, quency band than when the two loop sections are connected in series.

While any suitable switch means may be employed for thus connecting the two antenna's'ections either'in series or in parallel, I have herein shown a switch comprising two switch blades l8 and I9 pivotally mounted at and 2! and adapted when swung in one direction to connect the contacts 29 and 2! with other contacts 22 and 23, while when swung in the other direction, the switch blade [8 willconnect the contact 29 with the contact 24. The contact '22 is shown as being grounded on the chassis of 'the receiver and the shield of the loop as indicated at 25, and as alsobeing'connected to'the low potential end of the loop section 8 by a circuit connection 26. The high potential or hot? end of said loop section 8 is connected to the contact 24 by a circuit connection 21. The low potential end of the loop section 9 is connected, with the contact 28 by a circuit connection 28 and the high potential or hot? end of said loop section 9 is connected tothe circuit connection II, the latter also being connected to the contact 2| through a circuit connection 29.

When theswitch A is thrown so that the switch blade I8 connects the contacts20 and 22 and the switch blade I 9 connects the contacts 2| and 23, the two loop sections 8 and 9 will be connected in parallel, the circuit connection through the loop section 8 including the ground 25, the circuit connection 28, the loop section 8, the circuit connections 21 and 30, to contact 23, sw-itjch blade l9 and circuit connection 29 to the circuit connection I l. The circuit through the loop sec-V tion 9 is from the ground through the circuit connection 3 l.to contact 22, thence through the switch blade l8 to contact 29 and circuit connection 28 to the loop section 9 andthence to the circuit connection ll.

When the switch A is reversed and'the "switch blade [8 is in a position to connectthe contacts 20 and 24,-then the loop sectionsB and9' are connected in series, the circuit connection being from the ground 25,circuit-connection 26, loop section 8,-circuit connection 2 1,'switch' blade 18,

circuit connection 28 to loop section 9, and thence to the circuit connection ll.

' The two loop sections 8 and 9 are so disposed on the supporting frame that the hot or high potential end of each loop section is situated in the central portion of the frame as indicated best in Fig. 4, the low potential end of each loop section being at the outer ends of the section, that is, adjacent the side members 6 of the supporting frame. The supporting frame and the windings are enclosed in a suitable metallic shield 33, and one advantage resulting from this manner of disposing the loop sections relative to each other is that effective capacity to the shield is reduced.

The switch mechanism A for connecting the loop sections either in parallel or in series may have any suitable or usual construction and may be mounted either on the loop itself or on the receiver 2. I will preferably, however employ a switch constructed so that the two switch blades I8 and I 9 may be operated in unison 'from a single handle, and I will also preferably mou nt the switch on the loop itself as indicated in Fig. 1.

This construction has the advantage that the collector ring assembly is simplified and-the necessary conductors between the loop and the chassis are reduced to only a ground and 'one other wire. I

As stated above, connecting the loop sections either in parallel or in seriesf'enables the antenna loop to be used effectively on 'either oneiof; two difierent' frequency bands. By introducing a loading coil into the loop circuit, when the two loop sections are connected-in series, theloop inductance is so adjusted that theloop antenna can be efiectively used on a-frequency bandof still lower frequency than when the' loop sections are Y connected series but are not i used with the loading coil. l i One -way of connecting the'loadiii'coil into the circuit is illustrated in Figs. 2 and 4, this being done in connection with-a'band change switch B which may be installed in the receiver This band change switchis'shown as having two -stitcl1"blades 34 and. 35*connected in the circuit connection l2a; theswitch blade proper.

34 being adapted to engage any one of the three contacts 36, 31, 38 and the switch blade 35 being adapted: to engage anyone of the three contacts 39, 40, 4|. The contacts 36 and .39 are connected by a circuit connection 42,; the contacts 31 and 40 are connected by a-circuit connection 43 and the contacts 38 and 4| are connected byacircuit, connection 44 which hasthedoading coil 45 therein. The-switch B should Iceoperated in, conjunction with the switchA so ,that when the. switch A is adjusted to connect the loop sections;8 and 9 in parallel, the switch blades 34 and 35 will be in engagement with the contacts 36 and 39, thereby throwing 'a trimmer capacity 48 acrossfthe loop to enable it tobe properly tuned.'-

When the switch A is'adjusted to connectthe loop sections 8 and 9 in series, then '-the switch blades 34 and '35 will be broughtfintoffengagement with the contacts 31 and'40f therebylt'hrow connection 66, to the circuit-connection ll.

in which said antenna is fjormed of th threesection 50, and 52. These sections will be wound on the same supporting frame as in the construction shown in Fig. 4 and will therefore all be of the same dial'neter. The number of turns in each section may be varied as desired.

Where a loop made in three sections is' employed, I propose to provide a loop switch by means of which the three sections can be connected either in serie or in parallel or two of the sections may be connected in parallel but in series with the third section. This will. provide an antenna loop which will-operate eifectively on four diiferent frequency bands. I

Any suitable switch mechanismmay be employed for connectingth three loop sections in parallel or in series or partly in series and partly in parallel and as illustrative of a switch.mechanism suitable for this, I have shown one including the switch blades 53, 54, 55 and 56. The} and the circuit connections are such that trim.-

' mer capacity of an appropriate amount maybe-'1 thrown across the loop inthe different positionsg ofthe switch blades 34a and 35a.

The more turns there are in a loop-antenna for a given frequency band, the stronger will be the received signal "and the better the null indi cation." I By so making whentheloop is adjusted to operate on'any one of the various frequency ban s; there isprovided a [loop-antenna having the optimum number of turns "of the same diameter in the looplwinding which keeps the eifective height ofv the latter at a maximum for all of the frequencybands.

switch blade 53 is adapted to engage either of the contacts 51 or 58, the switch blade '54may be brought into engagement with the: contact 59.

The switch blade 55 may be brought into engagement with the contact 60 while the switch blade 56 may be engaged with either of the contacts 6! or 62. When the switch mechanism is set to connect the three loop sections 50, 5|, 52 in parallel, the switch blade 53 will be brought onto its contact 58, the switch blades 55 and'55 will be closed onto the contacts 59 and 60, while the switch blade55 is closed onto the contact 62. The circuit through the loop section 50 will include the'circuit C0117 nection 25, loop 50,-circuit connections 27 and 3E], switch 54 and circuit'connection 63 to the circuit connection II. The circuit through the loop section 5| will include circuit connection 3|, switch blade 53, circuit-connection 28, loop 51, circuit connection 55, switch blade .55 and circuit While I have shown the loop sections as having a different number of turns, yet the invention would not be departed-from if said 1001) sections weremade with the same number of turns as under some circumstances such afconstruction 3 would operate efliciently.

Iclaimg :1. A directional loop antenna structure for a radio direction finder, saidloop structure;c orr iprising'a rotatable'supporting frame, a-loop antennawound on said frame and comprising two" loop sections having. substantially the same die;

ameter and havinga common axis but having a 7 different number of turns, a singleshielding ele- The circuit through the loop section 52' will be circuit connections 3| and 67 to contact Bil, switch blade 55, circuit connection 68 to loop section 52 and thence to circuit connection I I.

By closing the switch blade 53 onto the contact 51 and opening the switch 54, the loop sections and 5! willbe connected in series but in parallel with the loop section 52.

By further adjusting the switch so as to open the switch and close the switch blade 56 onto the contact 5|, all three loop sections will be connected in series. i

Where a three-section antenna is employed, I propose to make the band change switch, which is indicated at Bl in Fig. 3, with four contact points as illustrated so that said switch may be set into four different positions, one forjeach of the four frequency bands for which the antenna loop may be adjusted.

The switch BI is shown as having two switch blades 34a and 35a that 'may be connected to move in unison, the Switchblade 36a being adapted. to contact with the contacts, H, 36a, 37a, 38a,

and the switch blade 35;; being adapted to en- 5 gage the contacts 12, 39a, 40a and (Ha. The circuit connection connecting the contacts 38a and Me has the loading coil 45a therein as in Fig. 2,

ment' enclosing both loop sections of said antenna, each loop section having its high poten 1 tial side on the end. there'ofadjacent. the other 1 section and itslow' potential sideat its outer end adiac'ent a wall of the shield,.whereby the capacity between the antenna winding and the shield isreduced, and meansfor connecting said loop sections either in parallel or in series.

2. A loop antenna for a radio direction finder,-

saidj antennacomprising two loop sections-all the turns of both sections having the same diameter. and having a'common axis, one loop section having a greater number of turns than the Q other, a single shielding element'enclosing both loop sections, the high potential end of each loop section being situated adjacent the highpotential end of the other loop section andthe low;

potential end of each loop section being situatedadjacent 'a wall of the shield whereby the'cae pacity' between the antenna, .winding and 1 the s I shield is reduced, and means for connecting said loop sections either in parallel or in series.- 3. Aloop antenna for a radio direction finder ,said antenna comprising two loop sections, all J the turns of both ,loop sections having substantially the same diameter and having a common axis, a singleshielding element enclosing both loop sections of saidfantenna, the windings of saidsections being arranged with the high. potential ends thereof situated between the low potential ends, whereby saidlowpotential ends'are nearer the walls of the shielding element than the high potential .ends,]and means for connectingsaid loop sections eitherin series or in parallel.

1 MARCUS 'G. LIMB.

the' loop that all the turns of, all, the loop sections areof substantiallylthe same" V a .diameter and are all included in the loop {circuit 

